This is the hollow shaft that runs on the main shaft. On preparing our racer twin for next season we found the clutch end had experienced some heating and the bush G17 slipped in and out with finger pressure. Good authorities tell me that there is a modification written somewhere detailing extra holes in the body of G4 and scalloping of the that end to increase lubrication which is restricted by the close association G12 and the washer G20/2 against the bushed clutch side end. I have had a good search for any info and drawn a blank can any one guide me to it?